Patent Application
20130283722
The present disclosure generally relates to tower structures and, more particularly, relates to transition structures for transitioning between adjacent, non-uniform tower sections for wind turbines.
A utility-scale wind turbine typically includes a set of two or three large rotor blades mounted to a hub. The rotor blades and the hub together are referred to as the rotor. The rotor blades aerodynamically interact with the wind and create lift, which is then translated into a driving torque by the rotor. The rotor is attached to and drives a main shaft, which in turn is operatively connected via a drive train to a generator or a set of generators that produce electric power. The main shaft, the drive train and the generator(s) may all be situated within a nacelle, which in turn is positioned on top of a wind turbine tower.
The wind turbine tower generally includes multiple tower sections, which may be transported individually by truck and/or rail to a wind turbine site and assembled together to form the tower. A steel tube tower is the most common wind turbine tower in use today and has, typically, three (3) to four (4) tower sections. As those of ordinary skill in this art are aware, each tower section comprises a top and a bottom annular flange, joined together by multiple cans which are individual plates of steel rolled and welded into the shape of a cylinder or a cone. Each can is welded to another can around its circumference to form a long tube, with the top can being welded to the top flange and the bottom can being welded to the bottom flange. Adjacent sections are joined together on-site by bolts that join the top flange of one section to the bottom flange of the next section.
A steel tube tower is the most economical tower option for a range of tower heights in many parts of the world today for a number of reasons. The steel tube tower has an attractive combination of material, manufacturing, transportation, and erection costs.
A typical steel tube tower for a wind turbine today ranges from sixty (60) meters to hundred (100) meters. As the height of such a tower increases, the base or bottom section of the tower must be increasingly strong and stiff to withstand the bending moments and loads. The strength and stiffness can be achieved basically by either increasing the diameter of the tower, or the thickness of the cans, or both. Increasing the diameter has transportation effects. For example, if the diameter becomes too large, the base tower section cannot be transported on public highways and roads or on railways to the site. For a very tall tower, if the base section diameter must be kept within practical transportation size constraints in order to limit transportation and erection costs, then the thickness of cans must be increased. But, the increased can thickness may result in substantially increased material and manufacturing costs.
As the desired height of wind turbine towers increases, a hybrid tower with a lattice bottom portion and a tube top portion looks increasingly attractive. A lattice bottom portion can be shipped to a site in several pieces and assembled to create a tower bottom portion with a large diameter or wide base. In some situations, a hybrid wind turbine tower with a lattice bottom and tube top may have the best combination of material, manufacturing, transportation, and erection costs. Several prior art patent applications and patents have proposed various iterations of hybrid lattice-tube towers, such as U.S. Pat. No. 7,276,808 B2 issued Oct. 2, 2007; U.S. Patent Application Publication No. 2008/0028715 A1 published Feb. 7, 2008; U.S. Patent Application Publication No. 2011/0146192 A1 published Jun. 23, 2011; German patent application publication DE 10 2004 020 480 A1, published Nov. 10, 2005; and German patent application publication DE 10 2005 047 961 A1, published Apr. 12, 2007.
With a hybrid lattice bottom, tube top tower an important element is the transition structure between the dissimilar tower portions. The loads must be effectively transferred from one portion of the tower to the other, and this can be difficult because the loads are carried in different ways by each portion of the tower. Many of the patents and published patent applications cited above are directed to proposed transition structures between the lattice bottom and the tube top portion. Of course, the transition structure should ideally consist of low cost materials, be simple to manufacture, and fast and easy to assemble on site.
The present disclosure describes a proposed transition structure between two dissimilar tower sections which may result in a tower with an attractive combination of material, manufacture, transportation, and erection costs.
In one embodiment, a transition structure for transitioning between two adjacent tower structures is disclosed. The transition structure may include a plurality of vertical legs, spaced apart from one another, a stub section positioned between an upper tower portion and a lower tower portion, a plurality of connecting members, each of the plurality of connecting members connecting one of the plurality of legs to the stub section and a torsion plate positioned between the plurality of vertical legs and the stub section.
In another embodiment, a transition structure for transitioning between two adjacent vertical tower structures is disclosed. The transition structure may include a plurality of vertical legs extending from a lower lattice tower portion, spaced circumferentially apart from one another, a tubular stub section connected to an upper tube tower portion and a plurality of connecting members, each of the plurality of connecting members connecting one of the plurality of vertical legs to the stub section. The transition structure may also include a torsion plate positioned vertically between the stub section and the upper tube tower portion, and extending radially between and connected to each of the stub section and each of the plurality of vertical legs.
In another embodiment, a wind turbine may include a wind turbine tower having an upper tower portion, a bottom tower portion having a plurality of vertical legs and a transition structure in between the upper tower portion and the bottom tower portion, the transition structure having a stub section, a plurality of connecting members connecting each of the plurality of vertical legs to the stub section and a torsion plate between the stub section and the plurality of vertical legs. The wind turbine may also include a rotor having a plurality of rotor blades and rotatably connected to a nacelle positioned on top of the upper tower portion.
Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.
For a more complete understanding of the disclosed methods and apparatuses, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein:
While the following detailed description has been given and will be provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims eventually appended hereto.
Referring to
With respect to the tower 4, in at least some embodiments, it may be a hybrid tower having a lower truss work or lattice work portion 14 mounted on or otherwise erected from a base foundation 16, and an upper tube portion 18 connected to the lower lattice portion 14 via a transition structure 20. The lattice portion 14 and the tube portion 18 may both be constructed from steel, or any other material suitable for use in a wind turbine tower. The lower lattice portion 14 may include a plurality of legs 22 between which a plurality of trusses may be connected to form a lattice structure in a known fashion. The diameter, height and pattern of the structure of the lattice portion 14 will vary depending upon factors such as the environment, the turbine loads, material costs, etc. The upper tube portion 18 may be constructed in a manner similar to modern wind turbine tube towers, with several sections each having a top and a bottom flange, joined together to form a tube. Or the tube portion 18 may be constructed in some other appropriate fashion. The tube portion 18 may be truly tubular in shape, with a constant diameter, or it may be somewhat tapered with a diameter that changes with height. Tube portion 18 might also conceivably have something other than a simple circular cross-section, it might comprise a shell with bends or flutes.
Referring now to
With respect to the plurality of legs 24, in at least some embodiments, each of the legs may be a structural member, such as an I-beam. In other embodiments, one or more of the legs may assume other configurations, such as C or other shaped channels and shells, or the legs may be other types of structural members. When an I-beam is used, the I-beam may be angularly positioned as shown, or in some embodiments, depending upon the configuration of the lattice portion 14, the I-beam may be vertically positioned. In at least some other embodiments, the legs 24 may be an extension of the legs 22 of the lattice portion 14 extending from the base foundation 16 up to the bottom of the tube portion 18 and following the angle of the legs 22. In yet other embodiments, the legs 24 may be connected to the legs 22. Additionally, while six of the legs 24 of the transition structure 20 have been shown, this is merely exemplary. In other embodiments, the number of legs 24 may vary from less than six to possibly even more depending upon the number of legs 22 of the lattice work section 14. It is contemplated that the number of legs 24 of the transition structure 20 may be equal to the number of legs 22 of the lattice portion 14. Also, and as illustrated in
As mentioned above, each of the legs 24 is connected to the stub section 26. The stub section 26 may be a tubular section, with same (or substantially same) diameter as the tube portion 18 and having a top flange 32 and a bottom flange 34. The top and the bottom flanges 32 and 34, respectively, of the stub section 26 may be employed for imparting stiffness to the stub section and the overall transition structure 20, as well for mounting to adjacent tower sections. For example, the top flange 32 may be joined to the torsion plate 30 between the stub section 26 and the tube portion 18 while the bottom flange 34 may be joined to the lattice portion 14 and a second torsion plate 52 (See
The stub section 26 may be connected to each of the legs 24 via the connecting member 28. As shown, each of the connecting members 28 may be a trapezoidal steel plate having a longitudinal vertical edge 40, a longitudinal slanting edge 42 and ringed all around with a steel plate edging 44 to form a beam shaped structure (for example, a broad I-beam). Notwithstanding the fact that the connecting member 28 is trapezoidal in shape and formed with the vertical edge 40 and the longitudinal slanting edge 42 in the illustrated embodiments, in at least some other embodiments, the connecting member and/or the various edges of the connecting member may assume other configurations, depending upon the shape of the stub section 26 and the angle of legs 24.
The longitudinal vertical edge 40 of each of the connecting members 28 may be connected to the stub section 26, while the longitudinal slanting edge 42 may be connected to the legs 24. In at least some embodiments, the edging 44 of the longitudinal vertical and slanting edges 40 and 42, respectively, of each of the connecting members 28 may be bolted to the stub section 26, as well as to a flange (e.g., flange of the I-beam) of the legs 24 by a plurality of bolts, exemplary locations of such bolts being represented by dashed lines 46 in
Referring still to
The transition structure 20 not only provides a way for transitioning from the tube portion 18 to the lattice portion 14 of the tower 4 of the wind turbine 2, it also provides rigidity to the tower and serves to effectively transfer forces from the tube portion to the lattice portion (and the surrounding ground). Specifically, any torsional forces may be transferred from the tube portion 18 to the torsion plate 30, which in turn may transfer those forces to the legs 24. From the legs 24, the torsional forces may be transferred to the legs 22 of the lattice portion 14, and from the lattice portion 14 of the tower 4 the torsional forces may be transferred to the surrounding ground via the base foundation 16.
In addition to torsional forces, the wind turbine 2 may be subjected to other types of loads such as bending loads, shear loads and axial loads. All these and other types of translational loads, as well as all moments, may be transferred primarily from the tube portion 18 to the lattice portion 14 via the legs 24, the connecting member 28 and the stub section 26. Specifically, the aforementioned loads may be transferred from the tube portion 18 to the stub section 26, and from the stub section to the legs 24 via the connecting members 28. From the legs 24 of the transition structure 20, all of the loads and moments may be transferred to the legs 22 of the lattice portion 14 and from the lattice portion to the base foundation 16 and the surrounding ground. Thus, the transition structure 20 transfers torsional forces primarily via the torsion plate 30 and all other translational loads and moments primarily via the stub section 26, the connecting members 28 and the legs 24.
Referring now to
Similar to the torsion plate 30, in at least some embodiments, the second torsion plate 52 may also be an annular disc, or may take the other forms described above with respect to torsion plate 30. The second torsion plate 50 may extend radially from the bottom flange 34 of the stub section 26 up to the bottom edging 44 of the connecting member 28, as shown in
In another embodiment, the torsion plate 30 may not be included while only torsion plate 52 is included. In addition to the components of the transition structure described above, in at least some embodiments, cross members connecting the legs of the transition structure may be employed depending upon the specific loads of the wind turbine, the wind turbine configuration and the hub height. Stiffener plates, as well as other stiffening components, may also be employed where deemed necessary by structural analysis.
The transition structures 20 and 50 may effectively be employed to transfer various loads (torsion, shear, bending and axial) including translational forces and all moments, from a top steel tube portion to a bottom lattice work portion of a wind turbine tower, while remaining easy to build and assemble. The transition structures 20 and 50 may be pre-assembled, for example by joining the torsion plate(s) with the stub section and the connecting members before transporting them to the site, or it may be assembled fairly easily on site. The transition structures 20 and 50 facilitate a wind turbine tower with a lattice work bottom portion, which can be transported in small pieces and assembled on site, thereby permitting larger diameter wind turbine tower bases.
Although the transition structures 20 and 50 has been described with respect to a wind turbine, in at least some embodiments, the transition structure may be employed in a variety of other structures where forces similar to those described above exist and a transmission of those forces between adjacent members is required. Furthermore, while the transition structure described above is employed to transition between a lattice portion and a steel tube portion, in other embodiments, the transition structure may be employed to transition between other types or shapes of tower portions. The transition structures 20 and 50 may also be employed to transition between different diameter tube tower portions such as between a wide diameter base tube portion at the bottom of the tower to smaller diameter middle or top tube portion. In addition, more than one transition structures 20 and/or 50 may possibly be used in one wind turbine tower.
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.
